Back to EveryPatent.com
United States Patent |
5,280,393
|
Kwon
|
January 18, 1994
|
Circuit for monitoring the recorded state of audio signal
Abstract
A circuit for monitoring the recorded state of audio signals from a
microphone on a magnetic tape. The circuit comprises an additional head
having only a playback function. The head functions to detect an audio
signal recorded on the magnetic tape. The detected audio signal is then
applied to an outer speaker, via a switch. Accordingly, the user can
monitor completely the recorded state of the audio signal on the magnetic
tape in the record mode operation of audio device.
Inventors:
|
Kwon; O Sang (Kangwon, KR)
|
Assignee:
|
Gold Star Co., Ltd. (KR)
|
Appl. No.:
|
777086 |
Filed:
|
October 16, 1991 |
Current U.S. Class: |
360/25 |
Intern'l Class: |
G11B 005/02; G11B 027/36 |
Field of Search: |
360/25,31,67,63-64,46,61,55
369/1-2
381/120-123,56
|
References Cited
U.S. Patent Documents
3879751 | Apr., 1975 | Gimelli | 360/31.
|
4245136 | Jan., 1981 | Krauel, Jr. | 381/56.
|
4412258 | Oct., 1983 | Shimada | 360/31.
|
Other References
Microelectronic Circuits by Adel S. Sedra and Kenneth C. Smith,
.COPYRGT.1987 CBS Publishing New York, N.Y., p. 8.
|
Primary Examiner: Sniezek; Andrew L.
Assistant Examiner: Pearson; Jennifer
Attorney, Agent or Firm: Poms, Smith, Lande & Rose
Claims
What is claimed is:
1. A circuit for monitoring the recorded state of an audio signal from a
microphone on a magnetic tape, comprising:
audio signal record and detect means for recording the audio signal on the
magnetic tape and detecting the audio signal recorded thereon;
audio signal detect means for detecting the audio signal recorded on the
magnetic tape, said audio signal detect means providing means for
monitoring the audio signal recorded on the magnetic tape;
first amplifying means for amplifying selectively the output from said
audio signal record and detect means and the output from said audio signal
detect means;
second amplifying means for amplifying the audio signal from the
microphone;
third amplifying means for amplifying selectively the output from said
first amplifying means or the output from the second amplifying means and
applying the amplified output to said audio signal record and detect
means, a speaker and an earphone; and
fourth amplifying means for amplifying selectively the audio signal from
the first amplifying means and applying the amplified output to a second
speaker or a second earphone.
2. A circuit in accordance with claim 1, wherein said audio signal detect
means comprises a head for detecting the audio signal recorded on the
magnetic tape, said head electronically connected to the second speaker or
second earphone, said second speaker or second earphone providing further
means for monitoring the audio signal recorded on the magnetic tape.
3. A circuit in accordance with claim 1, wherein said first amplifying
means comprises a first amplifying circuit for amplifying a signal
received therein, a first switch connected between said first amplifying
circuit and said audio signal record and detect means and adapted to be
switched for applying selectively the output from the audio signal record
and detect means, and a second switch connected between the first
amplifying circuit and the audio detect means and adapted to be switched
for applying selectively the output from the audio detect means to the
first amplifying circuit.
4. A circuit in accordance with claim 1, wherein said fourth amplifying
means comprises a filter for filtering a signal received therein, a second
amplifying circuit for amplifying the output from said filter, and a third
switch adapted to be switched for applying selectively the output from the
first amplifying means to the filter.
5. A circuit in accordance with claim 4, wherein said filter is a low pass
filter comprising a resistor and a capacitor.
6. A circuit for monitoring the recorded state of an audio signal from a
microphone on a magnetic tape, comprising:
audio signal record and detect means for recording the audio signal on the
magnetic tape and detecting the audio signal recorded thereon;
audio signal detect means for detecting the audio signal recorded on the
magnetic tape, said audio signal detect means comprising a head, said
audio signal detect means providing means for monitoring the audio signal
recorded on the magnetic tape;
first amplifying means for amplifying selectively the output from said
audio signal record and detect means and the output from said audio signal
record and detect means and the output from said audio signal detect
means, said first amplifying means comprising a first amplifying circuit
for amplifying a signal received therein, a first switch connected between
said first amplifying circuit and said audio signal record and detect
means and adapted to be switched for applying selectively the output from
the audio signal record and detect means, and a second switch connected
between the first amplifying circuit and the audio detect means and
adapted to be switched for applying selectively the output from the audio
detect means to the first amplifying circuit;
second amplifying means for amplifying the audio signal from the
microphone;
third amplifying means for amplifying selectively the output from said
first amplifying means or the output from the second amplifying means and
applying the amplified output to said audio signal record and detect
means, a speaker and an earphone, said third amplifying means including a
remover filter for filtering a signal received therein; and
fourth amplifying means for amplifying selectively the audio signal from
the first amplifying means and applying the amplified output to a second
speaker or a second earphone, said fourth amplifying means comprising a
low pass filter for filtering a signal received therein, a second
amplifying circuit for amplifying the output from said filter, and a third
switch adapted to be switched for applying selectively the output from the
first amplifying means to the filter, said low pass filter comprising a
resistor and a capacitor.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an audio device, and more particularly to
a circuit for monitoring the recording state of audio signals in a
magnetic tape.
2. Description of the Prior Art
As a widely used method for recording audio signals on a certain medium and
for playing back the recorded signals, there is a method in which electric
audio signals are stored in a magnetic tape as magnetic signals by using
an audio head, and if necessary, the magnetic signals are converted into
electric audio signals by the audio head again.
Referring to FIG. 1, there is shown a circuit diagram of a conventional
audio device in an audio head and a magnetic tape are utilized for
recording audio signals on the magnetic tape and playing back the recorded
audio signals. The audio device comprises an audio signal record and
detect circuit 100, a first amplifying circuit 200, a second amplifying
circuit 300, and a third amplifying circuit 400.
The audio signal record and detect circuit 100 which is adapted to
selectively record audio signals on a magnetic tape or detect them. That
is, the audio signal record and detect circuit 100 includes a mixer 10 to
which the output from the third amplifying circuit 400 is applied. The
mixer 10 comprises an oscillator 11 for oscillating a bias signal and an
adder 12 for mixing the output from the third amplifying circuit 400 and
the output from the oscillator 11. The audio signal record and detect
circuit 100 also includes a switch SW2 to which the mixer 10 is connected
so that its output is selectively applied to an audio head AHD, according
to the switching operation of the switch SW2. The circuit 100 also
comprises an audio head AHD for detecting signals recorded on the magnetic
tape.
The first amplifying circuit 200 comprises a switch SW1 for selectively
connecting the output of the audio signal record and detect circuit 100
and the first amplifying circuit 200 and an OP amplifier OP1 for
amplifying the output sent from the circuit 100 via the switch SW1.
The third amplifying circuit 400 comprises a switch SW3 connected at its
fixed terminals P and R with the output of the first amplifying circuit
200 and the output of the second amplifying circuit 300, respectively, and
OP amplifiers OP2, OP3 and OP4. In particular, the OP amplifier OP4 is
connected at its input and output to the OP amplifier OP2 and the mixer
10, respectively.
All of switches SW1 to SW3 are operatively connected with one another, as
shown in FIG. 1.
This device having the above-mentioned arrangement is operated in a record
mode for recording audio signals received from a microphone MIC on a
magnetic tape or in a playback mode for playing back the audio signals
recorded on the magnetic tape, for their listening. Now, the operation of
the device will be described in conjunction with respective modes.
1) RECORD MODE
When the audio device should be operated in its record mode, the user
operates switches SW1, SW2 and SW3 operatively connected with one another
so that their movable terminals are connected to the corresponding fixed
terminals R, respectively. Accordingly, an audio signal from the
microphone MIC is sent to the second amplifying circuit 300 and amplified
by the second amplifying circuit 300. The amplified audio signal is then
applied to the third amplifying circuit 400, via the switch SW3. The audio
signal applied to the third amplifying circuit 400 is amplified in the OP
amplifier OP2 which is a linear amplifier and then applied to OP
amplifiers OP3 and OP4.
The OP amplifier OP3 is a monitor amplifier which functions to amplify the
audio signal to the level suitable for driving an outer earphone EP or a
speaker SPK. On the other hand, the OP amplifier OP4 amplifies the audio
signal to the level suitable for recording it on the magnetic tape by an
audio head and applies the amplified audio signal to the mixer 10. The
adder 12 of mixer 10 mixes the output from the oscillator 11 generating a
bias signal with a certain frequency and the output from the OP amplifier
OP4. As a result, the audio signal from the microphone can be stored in
the magnetic tape by the audio head AHD and via the switch SW2 of the
audio signal record and detect circuit 100.
Since the audio signal from the microphone MIC is also sent to the outer
earphone, via the OP amplifier OP3, the user can check whether the audio
signal received from the microphone MIC is good, by listening to the sound
from the earphone.
2) PLAYBACK MODE
When the audio device should be operated in its playback mode, the user
operates switches SW1, SW2 and SW3 so that their movable terminals are
connected to the corresponding fixed terminals P, respectively.
Accordingly, an audio signal by the audio head AHD is sent to the first
amplifying circuit 200 via the switch SW1 and amplified by the OP
amplifier OP1 of the first amplifying circuit 200. The amplified audio
signal is then applied to the third amplifying circuit 400, via the switch
SW3. Thereby, the user can listen to the sound played back from the audio
signal recorded on the magnetic tape.
During the operation of the audio device in the playback mode, an audio
signal possibly sent from the microphone MIC is prevented from being
applied to the third amplifying circuit 400, by virtue of the switch SW3.
The switch SW2 functions to prevent the output from the mixer 10 to be
applied to the audio head AHD.
According to the arrangement of the conventional audio device, the user can
monitor whether an audio signal is outputted from the microphone, in that
in record mode operation, the third amplifying circuit amplifies the audio
signal from the microphone and sends the amplified audio signal to the
earphone. However, it is impossible to confirm whether the received audio
signal is correctly recorded on the magnetic tape by the audio head. If an
abnormality occurs at the mixer or the audio head, the audio signal can
not correctly recorded on the magnetic tape. In spite of this, the user
continuously attempts to operate the audio device in its record mode for
recording the audio signal on the magnetic tape, since he can not
recognize the abnormality by monitoring only the audio sound from the
earphone. As a result, he can recognize the record of no audio signal,
only under the playback mode operation of the audio device.
SUMMARY OF THE INVENTION
Therefore, it is an object of the invention to provide an audio device
including an additional head having only a playback function, thereby
capable of correctly monitoring the recorded state of audio signals on a
magnetic tape in its record mode operation.
According to the present invention, this object can be accomplished by
providing a circuit for monitoring the recorded state of an audio signal
from a microphone on a magnetic tape, comprising: audio signal record and
detect means for recording the audio signal on the magnetic tape and
detecting the audio signal recorded thereon; audio signal detect means for
detecting the audio signal recorded the magnetic tape; first amplifying
means for amplifying selectively the output from said audio signal record
and detect means and the output from said audio signal detect means;
second amplifying means for amplifying the audio signal from the
microphone; third amplifying means for amplifying selectively the output
from said first amplifying means or the output from the second amplifying
means and applying the amplified output to the audio signal record detect
means, a speaker and an earphone; and fourth amplifying means for
amplifying selectively the first amplifying means and applying the
amplified output to a second speaker or a second earphone.
BRIEF DESCRIPTION OF THE DRAWINGS
Other objects and aspects of the invention will become apparent from the
following description of embodiments with reference to the accompanying
drawings in which:
FIG. 1 Prior Art is a circuit diagram of a conventional audio device in
accordance with the prior art;
FIG. 2 is a circuit diagram of a device for monitoring the recorded state
of audio signals in accordance with the present invention; and
FIG. 3 is a schematic view of heads used in the monitoring circuit of the
present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring to FIG. 2, there is shown a circuit diagram of a device for
monitoring the recorded state of audio signals in accordance with the
present invention. The device comprises an audio signal record and detect
circuit 100, a first amplifying circuit 200, a second amplifying circuit
300, a third amplifying circuit 400, an audio signal detect circuit 500
and a fourth amplifying circuit 600.
The audio signal record and detect circuit 100 which is adapted to
selectively record audio signals on a magnetic tape or detect them has the
same arrangement as that of the above-described prior art circuit. That
is, the audio signal record and detect circuit 100 includes a mixer 10 to
which the output from the third amplifying circuit 400 is applied. The
mixer 10 comprises an oscillator 11 for oscillating a bias signal and an
adder 12 for mixing the output from the third amplifying circuit 400 and
the output from the oscillator 11. The audio signal record and detect
circuit 100 also includes a switch SW2 to which the mixer 10 is connected
so that its output is selectively applied to an audio head AHD, according
to the switching operation of the switch SW2. As shown in FIG. 3, the
audio head AHD comprises an audio signal record and detect head APRHD for
detecting signals recorded on the magnetic tape and an erase head EHD for
erasing signals recorded the magnetic tape.
FIG. 3 illustrates an example of video cassette recorders. In the drawing,
HD designates a video drum, FEHD an erase head for erasing image signals
recorded on a video tape VT, and the arrow the travel direction of the
video tape VT.
On the other hand, the audio signal detect circuit 500 is adapted to detect
audio signals recorded on the magnetic tape. As shown in FIG. 3, the audio
signal detect circuit 500 comprises an exclusive playback head PHD spaced
away from the audio head AHD and adapted to detect only audio signals
recorded on the magnetic tape.
The first amplifying circuit 200 is adapted to amplify selectively the
output from the audio signal record and detect circuit 100 or the output
from the audio signal detect circuit 500. To this end, the first
amplifying circuit 200 comprises a amplifying circuit 20 to which the
audio signal record and detect circuit 100 and the audio signal detect
circuit 500 are selectively connected, by means of switches SW1 and SW4,
respectively. The switch SW1 is selectively connected with the switch SW4.
The amplifying circuit 20 comprises an OP amplifier OP1, a filtering
capacitor C3 connected at both ends thereof to the inverting terminal-of
the OP amplifier OP1 via a resistor R3 and the output terminal of the OP
amplifier OP1, and a resistor R4 connected at both ends thereof to both
ends of the filtering capacitor C3, respectively. To the inverting
terminal of the OP amplifier OP1, a capacitor C2 for removing noise is
connected via a resistor R2. Between the connection of switches SW1 and
SW4 and the terminal + of the OP amplifier OP1, a capacitor C1 for cutting
off direct current is connected.
On the other hand, the second amplifying circuit 300 comprises an OP
amplifier OP6 connected at its terminal + with a microphone MIC. To the
inverting terminal of the OP amplifier OP6, a capacitor C4 for removing
noise is connected via a resistor R6. A resistor R5 is connected between
the output terminal and the inverting terminal--of the OP amplifier OP6.
The third amplifying circuit 400 is adapted to selectively amplify the
output from the first amplifying circuit 200 or the output from the second
amplifying circuit 300. To this end, the third amplifying circuit 400
comprises a switch SW3 connected at its fixed terminals P and R with the
first amplifying circuit 200 and the second amplifying circuit 300,
respectively. To the movable terminal of the switch SW3, a linear
amplifier OP2 is connected via a capacitor C5 for cutting off direct
current. A remover 1 which is a notch filter or an LC filter is connected
to the output of the OP amplifier OP2, via a capacitor C6 for cutting off
direct current. To the output of the remover 1, an OP amplifier OP3 is
connected which is adapted to amplify the signal from the remover 1 to the
level for driving an outer speaker SPK or an earphone EP.
The remover 1 of the third amplifying circuit 400 is connected with a
record amplifier OP4 which is connected at its output terminal to the
mixer 10.
On the other hand, the fourth amplifying circuit 600 is adapted to
selectively amplify the output from the first amplifying circuit 200 and
apply the amplified output to the outer speaker or the earphone. The
fourth amplifying circuit 600 comprises a switch SW5 connected at its
movable terminal to the output of the first amplifying circuit 200, a
filter 30 connected to the fixed terminal R of the switch SW5, and an
amplifying circuit 40 connected to the output of the filter 30. According
to the switching operation of the switch SW5, the output from the first
amplifying circuit 200 is selectively applied to the filter 30. The filter
30 is a low pass filter comprising a resistor R7 and a capacitor C7. On
the other hand, the amplifying circuit 40 comprises an OP amplifier OP5
connected at its terminal + to the filter 30 via a capacitor C8 for
cutting off direct current. To the inverting terminal--of the OP amplifier
OP5, a capacitor C9 for removing noise is connected via a resistor R8. A
resistor R9 is connected between the inverting terminal--and the output
terminal of the OP amplifier OP5. To the output terminal of the OP
amplifier OP5, a capacitor C10 is also connected.
All of switches SW1 to SW5 according to the present invention are
operatively connected, although not shown in the drawings.
The audio device having the above-mentioned arrangement according to the
present invention is operated in its record mode or playback mode. The
operation of the device will now be described in conjunction with the
respective modes.
1) RECORD MODE
When the audio device should be operated in its record mode, the user
operates switches SW1 to SW5 so that their movable terminals are connected
to the corresponding fixed terminals R, respectively. As the switch SW3 is
switched to its fixed terminal R, an audio signal from the microphone MIC
is received in the second amplifying circuit 300 and amplified by the OP
amplifier OP6. The amplified audio signal is sent to the third amplifying
circuit 400 and amplified again by the OP amplifier OP2. At this time, the
horizontal synchronizing component of the output of OP amplifier OP2 is
removed by the remover 1. The result signal is amplified again by the OP
amplifier OP3 and then outputted to the outer speaker SPK or the earphone
EP so that the user can monitor the audio signal received from the
microphone MIC.
On the other hand, the audio signal from the remover 1 is also amplified by
the OP amplifier OP4 and then applied to the adder 12 of the mixer 10. In
the adder 12, the audio signal is mixed with a bias signal of a
predetermined frequency oscillated from the oscillator 11 and applied to
the adder 12. The output from the adder 12 is sent to the switch SW2. At
this time, the switch SW2 is at the state that its movable terminal is
connected to its fixed terminal R, thereby enabling the audio signal from
the mixer 10 to be recorded on the magnetic tape by the audio head AHD.
The playback head PHD which is spaced away from the audio head AHD as shown
in FIG. 3 detects the audio signal which has been recorded on the magnetic
tape by the audio head AHD.
The audio signal detected by the playback head PHD is applied the first
amplifying circuit 200, since the switch SW4 is at the state that its
movable terminal is connected to its fixed terminal R. At this time, the
switch SW1 is also at the state that its movable terminal is connected to
its fixed terminal R. Accordingly, the audio signal from the audio head
AHD does not affect the first amplifying circuit 200. The audio signal
from the playback head PHD applied to the first amplifying circuit 200 is
amplified by the OP amplifier OP1 and then compensated for low frequency
by the capacitor C3 and the resistor R4. At this time, the switch SW4 is
at the state that its movable terminal is connected to its fixed terminal
R. Accordingly, the output from the first amplifying circuit 100 does not
affect the third amplifying circuit 400. Since the switch SW5 is at the
state that its movable terminal is connected to its fixed terminal R, the
noise of the high frequency component of the audio signal from the first
amplifying circuit 200 is removed by the resistor R7 and the capacitor C7.
The result signal is amplified by the OP amplifier OP5 and then outputted
to an outer terminal O-P. By connecting the speaker or the earphone to the
outer terminal O-P, therefore, the user can monitor whether the audio
signal from the microphone MIC is correctly recorded by the audio head
AHD.
2) PLAYBACK MODE
When the audio device should be operated in its playback mode, so as to
play back the audio signal recorded on the magnetic tape and listen to the
sound, the user operates switches SW1 to SW3 so that their movable
terminals are connected to the corresponding fixed terminals P,
respectively. Since the switch SW2 is switched to its fixed terminal P,
the output from the mixer 10 is not applied to the audio head AHD so that
the audio head AHD detects completely the audio signal from the magnetic
tape and applies it to the switch SW1.
Switches SW1 and SW4 are also at the state that their movable terminals are
connected to their fixed terminals P. Accordingly, the audio signal from
the audio head AHD is amplified by the first amplifying circuit 200. At
this time, the first amplifying circuit 200 amplifies completely the audio
signal from the audio head AHD, in that the audio signal detected by the
playback head PHD can not be applied to the amplifying circuit 20 of the
first amplifying circuit 200, due to the switched condition of the switch
SW4.
As above, the audio signal from the playback head PHD should not be applied
to the first amplifying circuit 200. If the audio signal from the audio
head AHD and the audio signal from the playback head PHD are
simultaneously applied to the first amplifying circuit 200, they may be
mixed with each other, so that a complete sound reproduction may be
impossible.
Since switches SW3 and SW5 are also at the state that their movable
terminals are connected to their fixed terminals P, the audio signal
amplified by the first amplifying circuit 200 is amplified by the OP
amplifiers OP2 and OP3 of the third amplifying circuit 400. The amplified
audio signal is then outputted to the outer speaker SPK or the earphone EP
so that the user can listen to the audio signal detected from the magnetic
tape.
At this time, the audio signal from the microphone MIC and the audio signal
from the first amplifying circuit 200 are cut off by the switch SW3 and
the switch SW5, respectively, so that the user can not listen to those
audio signals.
If necessary, the switch SW5 may be switched to its fixed terminal R, even
in the playback mode operation of the audio device. In this case, the user
can listen to the audio signal by utilizing the outer terminal O-P.
As apparent from the above description, the present invention provides an
audio device in which a playback head is positioned near an audio head, so
that the user can listen to an audio signal recorded on a magnetic tape in
the record mode operation, by utilizing switches and an audio signal
outputting circuit. Accordingly, it is possible to monitor whether the
audio signal is completely recorded on the magnetic tape.
Although the preferred embodiments of the invention have been disclosed for
illustrative purpose, those skilled in the art will appreciated that
various modifications, additions and substitutions are possible, without
departing from the scope and spirit of the invention as disclosed in the
accompanying claims.
Top